Rare earth reduced garnet systems and related microwave applications

ABSTRACT

Disclosed are synthetic garnets and related devices that can be used in radio-frequency (RF) applications. In some embodiments, such RF devices can include garnets having reduced or substantially nil Yttrium or other rare earth metals. Such garnets can be configured to yield high dielectric constants, and ferrite devices, such as TM-mode circulators/isolators, formed from such garnets can benefit from reduced dimensions. Further, reduced or nil rare earth content of such garnets can allow cost-effective fabrication of ferrite-based RF devices. In some embodiments, such ferrite devices can include other desirable properties such as low magnetic resonance linewidths. Examples of fabrication methods and RF-related properties are also disclosed.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND

Field

The present disclosure generally relates to synthetic garnet systems andrelated radio-frequency (RF) applications.

Description of the Related Art

Various crystalline materials with magnetic properties have been used ascomponents in electronic devices such as cellular phones, biomedicaldevices, and RFID sensors. Garnets are crystalline materials withferrimagnetic properties particularly useful in RF electronics operatingin the lower frequency portions of the microwave region. Many microwavemagnetic materials are derivatives of Yttrium Iron Garnet (YIG), asynthetic form of garnet widely used in various telecommunicationdevices largely because of its favorable magnetic properties such asnarrow line absorption at its ferromagnetic resonance frequency. YIG isgenerally composed of Yttrium, Iron, Oxygen, and possibly doped with oneor more other rare earth metals such as the Lanthanides or Scandium.However, the supply of rare earth elements such as Yttrium has recentlybecome increasingly restricted, thus resulting in correspondingly steepincreases in cost. As such, there is a need to find a cost-effectivesubstitute for rare earth elements in synthetic garnet structures thatdoes not compromise the magnetic properties of the material and can beused for microwave applications.

SUMMARY

The compositions, materials, methods of preparation, devices, andsystems of this disclosure each have several aspects, no single one ofwhich is solely responsible for its desirable attributes. Withoutlimiting the scope of this invention, its more prominent features willnow be discussed briefly.

Any terms not directly defined herein shall be understood to have all ofthe meanings commonly associated with them as understood within the art.Certain terms are discussed below, or elsewhere in the specification, toprovide additional guidance to the practitioner in describing thecompositions, methods, systems, and the like of various embodiments, andhow to make or use them. It will be appreciated that the same thing maybe said in more than one way. Consequently, alternative language andsynonyms may be used for any one or more of the terms discussed herein.No significance is to be placed upon whether or not a term is elaboratedor discussed herein. Some synonyms or substitutable methods, materialsand the like are provided. Recital of one or a few synonyms orequivalents does not exclude use of other synonyms or equivalents,unless it is explicitly stated. Use of examples in the specification,including examples of terms, is for illustrative purposes only and doesnot limit the scope and meaning of the embodiments herein.

Embodiments disclosed herein include methods for modifying syntheticgarnets used in RF applications to reduce or eliminate Yttrium (Y) orother rare earth metals in the garnets without adversely affecting themagnetic properties of the material. In some embodiments, modifiedsynthetic garnet compositions with significantly reduced rare earthcontent are designed with properties suitable for use as ferritematerials in devices such as isolators and circulators, which arenecessary components in all cellular base stations.

Some embodiments include methods of substituting at least some of theYttrium (Y) in a garnet structure with other chemicals, such as acombination of Bismuth and one or more high valency ions. The substitutechemicals are selected to reduce the content of Y without adverselyaffecting the performance of the material. The rare earth substitutionsdescribed herein substantially reduce the need for Yttrium Oxides in thesynthesis of certain garnet structures such as Yttrium Iron Garnets(YIG), and provide modified crystalline materials useful in a variety ofelectronic applications including but not limited to uses in devices forcellular base stations.

In one embodiment, the method for modifying synthetic garnets comprisessubstituting Bismuth (Bi) for some of the Yttrium (Y) on thedodecahedral sites of the garnet structure and introducing high valencynon-magnetic ions, preferably greater than +3, to the octahedral sitesto replace some of the Iron (Fe) in the garnet. The quantity andcombination of substitute ions and processing techniques are selected toensure that the resulting material has high magnetization with lowlinewidth, along with reduced Yttrium (Y) content. In some embodiments,Calcium (Ca) is also introduced to the dodecahedral sites of the garnetstructure for charge compensation induced by the high valency ions whileat the same time replace some or all of the remaining Yttrium (Y). Insome other embodiments, the method further comprises introducing one ormore high valency ions, such as Vanadium (V⁵⁺), to the tetrahedral sitesof the garnet structure to further reduce the saturation magnetizationof the resulting material.

In one implementation, the modified synthetic crystalline material isrepresented by the formulaBi_(x)Ca_(y+2x)Y_(1−x−y−2z)Fe_(5−y−z)Zr_(y)V_(z)O₁₂, wherein x isgreater than or equal to 0.5 and less than or equal to 1.4, y is greaterthan or equal to 0.3 and less than or equal to 0.55, and z is greaterthan or equal to 0 or less than or equal to 0.6. Bi and Ca are placed onthe dodecahedral sites, Zr is placed on the octahedral sites, and V isplaced on the tetrahedral sites. In some versions, small amounts ofNiobium (Nb) may be placed on the octahedral site and small amounts ofMolybdenum (Mo) on the tetrahedral site. Preferably, the modifiedcrystalline material has a magnetic resonance linewidth of less than orequal to 11 Oersted.

In another embodiment, the modified synthetic crystalline material isrepresented by the formula Bi(Y,Ca)₂Fe_(4.2)M^(I) _(0.4)M^(II)_(0.4)O₁₂, where M^(I) is the octahedral substitution for Fe and can beselected from the group consisting of In, Zn, Mg, Zr, Sn, Ta, Nb, Fe,Ti, Sb, and combinations thereof where M^(II) is the tetrahedralsubstitution for Fe and can be selected from the group consisting of:Ga, W, Mo, Ge, V, Si, and combinations thereof.

In yet another implementation, the modified synthetic crystallinematerial is represented by the formulaBi_(0.9)Ca_(0.9x)Y_(2.1−0.9x)(Zr_(0.7)Nb_(0.1))_(x)Fe_(5−0.8x)O₁₂,wherein x is greater than or equal to 0.5 and less than or equal to 1.0.

In yet another implementation, the modified synthetic crystallinematerial is represented by the formulaBi_(x)Y_(3−x−0.35)Ca_(0.35)Zr_(0.35)Fe_(4.65)O₁₂, where x is greaterthan or equal to 0.5 and less than or equal to 1.0, more preferably x isgreater or equal to 0.6 and less than or equal to 0.8.

In yet another implementation, the modified synthetic crystallinematerial is represented by the formulaY_(2.15−2x)Bi_(0.5)Ca_(0.35+2x)Zr_(0.35)V_(x)Fe_(4.65−x)O₁₂, wherein xis greater than or equal to 0.1 and less than or equal to 0.8.

In yet another implementation, a modified Yttrium based garnet structureis provided. The modified Yttrium based garnet structure comprisesBismuth (Bi³⁺) and Calcium (Ca²⁺) doped dodecahedral sites, andtetravalent or pentavalent ion doped octahedral sites, wherein Bi³⁺occupies about 0 to 100 atomic percent of the dodecahedral sites, Ca²⁺occupies about 0 to 90 atomic percent of the dodecahedral sites, whereinthe tetravalent or pentavalent ions occupy about 0 to 50 atomic percentof the octahedral sites, wherein said modified synthetic Yttrium basedgarnet structure has a magnetic resonance linewidth of between 0 and 50Oersteds. In some implementations, the modified Yttrium based garnetstructure further comprises Vanadium (V⁵⁺) doped tetrahedral sites,wherein V⁵⁺ occupies about 0 to 50 atomic percent of the tetrahedralsites. Preferably, Yttrium occupies the balance of the dodecahedralsites of the modified Yttrium based garnet structure. In someimplementations, the modified Yttrium based garnet structure isincorporated as a ferrite material in RF devices such isolators,circulators, or resonators.

Advantageously, the substitution allows the use of tetravalent,pentavalent, and other ions on the octahedral site of the garnetstructure, resulting in potentially high magnetization with lowlinewidth, along with reduced Y content.

In some implementations, the present disclosure relates to a syntheticgarnet material having a structure including dodecahedral sites, withBismuth occupying at least some of the dodecahedral sites. The garnetmaterial has a dielectric constant value of at least 21.

In some embodiments, the dielectric constant value can be in a range of25 to 32. In some embodiments, the garnet can be represented by theformula Bi_(3−x)(RE or Ca)_(x)Fe_(2−y)(Me)_(y)Fe_(3−z)(Me′)_(z)O₁₂ wherex is greater than or equal to 1.6 and less than or equal to 2.0, RErepresents a rare earth element, and each of Me and Me′ represents ametal element. The value of x can be approximately 1.6. The metalelement Me can include Zr and the value of y can be greater than orequal to 0.35 and less than or equal to 0.75. The value of y can beapproximately 0.55. The metal element Me′ can include V and the value ofz can be greater than or equal to 0 and less than or equal to 0.525. Thevalue of z can be approximately 0.525 such that the garnet issubstantially free of rare earth and the formula isBi_(1.4)Ca_(1.6)Zr_(0.55)V_(0.525)Fe_(3.925)O₁₂. For such an examplecomposition, the dielectric constant value can be approximately 27. Insome embodiments, the garnet material can have a ferrimagnetic resonancelinewidth value that is less than 12 Oersted.

According to a number of implementations, the present disclosure relatesto a method for fabricating synthetic garnet material havingdodecahedral sites, octahedral sites, and tetrahedral sites. The methodincludes introducing Bismuth into at least some of the dodecahedralsites. The method further includes introducing high-polarization ionsinto at least some of either or both of the octahedral and tetrahedralsites to yield a dielectric constant value of at least 21 for the garnetmaterial.

In some embodiments, the high-polarization ions can include non-magneticions. The non-magnetic ions can include Zirconium in octahedral sites inconcentration selected to maintain a low magnetic resonance linewidth.The magnetic resonance linewidth can be less than or equal to 12Oersted. The non-magnetic ions can include Vanadium in tetrahedralsites.

In some embodiments, the dielectric constant value can be in a range of25 to 32. In some embodiments, the introduction of Bismuth andhigh-polarization ions can result in the garnet material beingsubstantially free of rare earth.

In a number of implementations, the present disclosure can include acirculator that includes a conductor having a plurality of signal ports.The circulator further includes one or more magnets configured toprovide a magnetic field. The circulator further includes one or moreferrite disks disposed relative to the conductor and the one or moremagnets so that a radio-frequency (RF) signal is routed selectivelyamong the signal ports due to the magnetic field. Each of the one ormore ferrite disks has an enhanced dielectric constant value of at least21 and at least some garnet structures. The garnet structures includedodecahedral sites, and at least some of the dodecahedral sites areoccupied by Bismuth.

In some embodiments, the garnet structures can be substantially free ofYttrium. In some embodiments, the garnet structures can be substantiallyfree of rare earth elements.

In some embodiments, the ferrite disk can be a circular shaped disk. Insome embodiments, the circular shaped ferrite disk can have a diameterthat is reduced by a factor of square root of (ε/ε′), where ε is thedielectric constant in a range of 14 to 16, and ε′ is the enhanceddielectric constant. In some embodiments, the circulator can be atransverse magnetic (TM) mode device.

In accordance with some implementations, the present disclosure relatesto a packaged circulator module that includes a mounting platformconfigured to receive one or more components thereon. The packagedcirculator module further includes a circulator device mounted on themounting platform. The circulator device includes a conductor having aplurality of signal ports. The circulator device further includes one ormore magnets configured to provide a magnetic field. The circulatorfurther includes one or more ferrite disks disposed relative to theconductor and the one or more magnets so that a radio-frequency (RF)signal is routed selectively among the signal ports due to the magneticfield. Each of the one or more ferrite disks has an enhanced dielectricconstant value of at least 21 and at least some garnet structures. Thegarnet structures include dodecahedral sites and at least some thereofoccupied by Bismuth. The packaged circulator module further includes ahousing mounted on the mounting platform and dimensioned tosubstantially enclose and protect the circulator device.

In some implementations, the present disclosure relates to aradio-frequency (RF) circuit board that includes a circuit substrateconfigured to receive a plurality of components. The circuit boardfurther includes a plurality of circuits disposed on the circuitsubstrate and configured to process RF signals. The circuit boardfurther includes a circulator device disposed on the circuit substrateand interconnected with at least some of the circuits. The circulatordevice includes a conductor having a plurality of signal ports. Thecirculator device further includes one or more magnets configured toprovide a magnetic field. The circulator further includes one or moreferrite disks disposed relative to the conductor and the one or moremagnets so that a radio-frequency (RF) signal is routed selectivelyamong the signal ports due to the magnetic field. Each of the one ormore ferrite disks has an enhanced dielectric constant value of at least21 and at least some garnet structures. The garnet structures includedodecahedral sites and at least some thereof occupied by Bismuth. Thecircuit board further includes a plurality of connection featuresconfigured to facilitate passing of the RF signals to and from the RFcircuit board.

According to some implementations, the present disclosure relates to aradio-frequency (RF) system that includes an antenna assembly configuredto facilitate transmission and reception of RF signals. The systemfurther includes a transceiver interconnected to the antenna assemblyand configured to generate a transmit signal for transmission by theantenna assembly and process a received signal from the antennaassembly. The system further includes a front end module configured tofacilitate routing of the transmit signal and the received signal. Thefront end module includes one or more circulators, with each circulatorincluding a conductor having a plurality of signal ports. The circulatorfurther includes one or more magnets configured to provide a magneticfield. The circulator further includes one or more ferrite disksdisposed relative to the conductor and the one or more magnets so that aradio-frequency (RF) signal is routed selectively among the signal portsdue to the magnetic field. Each of the one or more ferrite disks had anenhanced dielectric constant value of at least 21 and at least somegarnet structures. The garnet structures include dodecahedral sites andat least some thereof occupied by Bismuth.

In some embodiments, the system can include a base station. In someembodiments, the base station can include a cellular base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows how materials having one or more featuresdescribed herein can be designed, fabricated, and used.

FIG. 2 depicts a Yttrium based garnet crystal lattice structure;

FIG. 3 is an example graph depicting variations of material propertiesversus varying levels of Vanadium in crystalline compositionsrepresented by the formulaY_(2.15−2x)Bi_(0.5)Ca_(0.35+2x)Zr_(0.35)V_(x)Fe_(4.65−x)O₁₂, where x=0.1to 0.8.

FIG. 4 is an example graph depicting variations of material propertiesversus varying levels of (Zr, Nb) in crystalline compositionsrepresented by the formulaBi_(0.9)Ca_(0.9x)Y_(2.1−0.9x)(Zr_(0.7)Nb_(0.1))_(x)Fe_(5−0.8x)O₁₂, wherex=0.5 to 1.0.

FIGS. 5A-5G are example graphs depicting the relationship between firingtemperature and various properties at varying levels of Vanadium incrystalline compositions represented by the formulaBi_(0.9)Ca_(0.9+2x)Zr_(0.7)Nb_(0.1)V_(x)Fe_(4.2−x)O₁₂ where x=0-0.6.

FIG. 6 is an example graph depicting best linewidth versus compositionof varying Vanadium content in crystalline compositions represented bythe formula Bi_(0.9)Ca_(0.9+2x)Zr_(0.7)Nb_(0.1)V_(x)Fe_(4.2−x)O₁₂ wherex=0-0.6.

FIG. 7 is an example graph illustrating the properties of crystalcompositions represented by the formulaBi_(1.4)Ca_(1.05−2x)Zr_(0.55)V_(x)Fe_(4.45−x)O₁₂, where x=0-0.525.

FIG. 8 illustrates an example process flow for making a modifiedsynthetic garnet having one or more features described herein.

FIG. 9 shows an example ferrite device having one or more garnetfeatures as described herein.

FIG. 10 shows various properties as functions of Zr content for anexample composition Bi_(0.5)Y_(2.5−x)Ca_(x)Zr_(x)Fe_(5−x)O₁₂ where Bi⁺³content is substantially fixed at approximately 0.5 while Zr⁺⁴ contentis varied from 0 to 0.35.

FIG. 11 shows various properties as functions of Bi content for anexample composition Bi_(x)Y_(2.65−x)Ca_(0.35)Zr_(0.35)Fe_(4.65)O₁₂ whereZr⁺⁴ content is substantially fixed at approximately 0.35 while Bi⁺³content is varied.

FIG. 12 shows dielectric constant and density as functions of Bi contentfor the example composition of FIG. 11.

FIG. 13 shows plots of various properties as functions of Zr contentthat extends beyond the 0.35 limit of the example composition of FIG.10.

FIG. 14 shows plots of various properties as functions of V⁺⁵ contentwhen Bi content is approximately 1.4 and Zr content is approximately0.55 for the example composition of FIG. 13.

FIGS. 15A and 15B show examples of size reduction that can beimplemented for ferrite devices having one or more features as describedherein.

FIGS. 16A and 16B show an example circulator/isolator having ferritedevices as described herein.

FIG. 17 shows insertion loss plots and return loss plots for two example25 mm circulators, where one is based on a YCaZrVFe garnet system withdielectric constant of 14.4, and another is based on a Yttrium freeBiCaZrVFe garnet system with dielectric constant of 26.73.

FIGS. 18A and 18B show s-parameter data for an example 10 mm circulatordevice having the high-dielectric Yttrium free BiCaZrVFe garnet systemof FIG. 17.

FIG. 19 shows an example of a packaged circulator module.

FIG. 20 shows an example RF system where one or more ofcirculator/isolator devices as described herein can be implemented.

FIG. 21 shows a process that can be implemented to fabricate a ceramicmaterial having one or more features as described herein.

FIG. 22 shows a process that can be implemented to form a shaped objectfrom powder material described herein.

FIG. 23 shows examples of various stages of the process of FIG. 22.

FIG. 24 shows a process that can be implemented to sinter formed objectssuch as those formed in the example of FIGS. 22 and 23.

FIG. 25 shows examples of various stages of the process of FIG. 24.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

FIG. 1 schematically shows how one or more chemical elements (block 1),chemical compounds (block 2), chemical substances (block 3) and/orchemical mixtures (block 4) can be processed to yield one or morematerials (block 5) having one or more features described herein. Insome embodiments, such materials can be formed into ceramic materials(block 6) configured to include a desirable dielectric property (block7), a magnetic property (block 8) and/or an advanced material property(block 9).

In some embodiments, a material having one or more of the foregoingproperties can be implemented in applications (block 10) such asradio-frequency (RF) application. Such applications can includeimplementations of one or more features as described herein in devices12. In some applications, such devices can further be implemented inproducts 11. Examples of such devices and/or products are describedherein.

Disclosed herein are methods of modifying synthetic garnet compositions,such as Yttrium Iron Garnet (YIG), to reduce or eliminate the use ofrare earth metals in such compositions. Also disclosed herein aresynthetic garnet materials having reduced or no rare earth metalcontent, methods of producing the materials, and the devices and systemsincorporating such materials. The synthetic garnet materials preparedaccording to embodiments described in the disclosure exhibit favorablemagnetic properties for microwave magnetic applications. These favorableproperties include but are limited to low magnetic resonance line width,optimized density, saturation magnetization and dielectric loss tangent.Applicants have surprisingly found that when garnet compositions aredoped with certain combinations of ions and prepared using certainprocessing techniques, a significant amount if not all of the rare earthelements can be substituted and yet still result in microwave magneticcrystalline materials with comparable, if not superior, performancecharacteristics as commercially available garnets containing Yttrium (Y)or other rare earth elements.

Synthetic garnets typically have the formula unit of A₃B₅O₁₂, where Aand B are trivalent metal ions. Yttrium Iron Garnet (YIG) is a syntheticgarnet having the formula unit of Y₃Fe₅O₁₂, which includes Yttrium (Y)in the 3+ oxidation state and Iron (Fe) in the 3+ oxidation state. Thecrystal structure of a YIG formula unit is depicted in FIG. 2. As shownin FIG. 2, YIG has a dodecahederal site, an octahedral site, and atetrahedral site. The Y ions occupy the dodecahedral site while the Feions occupy the octahedral and tetrahedral sites. Each YIG unit cell,which is cubic in crystal classifications, has eight of these formulaunits.

The modified synthetic garnet compositions, in some embodiments,comprise substituting some or all of the Yttrium (Y) in Yttrium IronGarnets (YIG) with a combination of other ions such that the resultingmaterial maintains desirable magnetic properties for microwaveapplications. There have been past attempts toward doping YIG withdifferent ions to modify the material properties. Some of theseattempts, such as Bismuth (Bi) doped YIG, are described in “MicrowaveMaterials for Wireless Applications” by D. B. Cruickshank, which ishereby incorporated by reference in its entirety. However, in practiceions used as substitutes may not behave predictably because of, forexample, spin canting induced by the magnetic ion itself or by theeffect of non-magnetic ions on the environment adjacent magnetic ions,reducing the degree alignment. Thus, the resulting magnetic propertiescannot be predicted. Additionally, the amount of substitution is limitedin some cases. Beyond a certain limit, the ion will not enter itspreferred lattice site and either remains on the outside in a secondphase compound or leaks into another site. Additionally, ion size andcrystallographic orientation preferences may compete at highsubstitution levels, or substituting ions are influenced by the ion sizeand coordination of ions on other sites. As such, the assumption thatthe net magnetic behavior is the sum of independent sub-lattices orsingle ion anisotropy may not always apply in predicting magneticproperties.

Considerations in selecting an effective substitution of rare earthmetals in YIG for microwave magnetic applications include theoptimization of the density, the magnetic resonance linewidth, thesaturation magnetization, the Curie temperature, and the dielectric losstangent in the resulting modified crystal structure. Magnetic resonanceis derived from spinning electrons, which when excited by an appropriateradio frequency (RF) will show resonance proportional to an appliedmagnetic field and the frequency. The width of the resonance peak isusually defined at the half power points and is referred to as themagnetic resonance linewidth. It is generally desirable for the materialto have a low linewidth because low linewidth manifests itself as lowmagnetic loss, which is required for all low insertion loss ferritedevices. The modified garnet compositions according to preferredembodiments of the present invention provide single crystal orpolycrystalline materials with reduced Yttrium content and yetmaintaining low linewidth and other desirable properties for microwavemagnetic applications.

In some embodiments, a Yttrium based garnet is modified by substitutingBismuth (Bi³⁺) for some of the Yttrium (Y³⁺) on the dodecahedral sitesof the garnet structure in combination with introducing one or moreions, such as divalent (+2), trivalent (+3), tetravalent (+4),pentavalent (+5) or hexavalent (+6) non-magnetic ions to the octahedralsites of the structure to replace at least some of the Iron (Fe³⁺). In apreferred implementation, one or more high valency non-magnetic ionssuch as Zirconium (Zr⁴⁺) or Niobium (Nb⁵⁺) can be introduced to theoctahedral sites.

In some embodiments, a Yttrium based garnet is modified by introducingone or more high valency ions with an oxidation state greater than 3+ tothe octahedral or tetrahedral sites of the garnet structure incombination with substituting Calcium (Ca²⁺) for Yttrium (Y³⁺) in thedodecahedral site of the structure for charge compensation induced bythe high valency ions, hence reducing the Y³⁺ content. Whennon-trivalent ions are introduced, valency balance is maintained byintroducing, for example, divalent Calcium (Ca²⁺) to balance thenon-trivalent ions. For example, for each 4+ ion introduced to theoctahedral or tetrahedral sites, one Y³⁺ ion is substituted with a Ca²⁺ion. For each 5+ ion, two Y³⁺ ions are replaced by Ca²⁺ ions. For each6+ ion, three Y³⁺ ions are replaced by Ca²⁺ ions. For each 6+ ion, threeY³⁺ ions are replaced by Ca²⁺ ions. In one implementation, one or morehigh valence ions selected from the group consisting of Zr⁴⁺, Sn⁴⁺,Ti⁴⁺, Nb⁵⁺, Ta⁵⁺, Sb⁵⁺, W⁶⁺, and Mo⁶⁺ is introduced to the octahedral ortetrahedral sites, and divalent Calcium (Ca²⁺) is used to balance thecharges, which in turn reduces Y³⁺ content.

In some embodiments, a Yttrium based garnet is modified by introducingone or more high valency ions, such as Vanadium (V⁵⁺), to thetetrahedral site of the garnet structure to substitute for Fe³⁺ tofurther reduce the magnetic resonance linewidth of the resultingmaterial. Without being bound by any theory, it is believed that themechanism of ion substitution causes reduced magnetization of thetetrahedral site of the lattice, which results in higher netmagnetization of the garnet, and by changing the magnetocrystallineenvironment of the ferric ions also reduces anisotropy and hence theferromagnetic linewidth of the material.

In some embodiments, Applicant has found that a combination of highBismuth (Bi) doping combined with Vanadium (V) and Zirconium (Zr)induced Calcium (Ca) valency compensation could effectively displace allor most of the Yttrium (Y) in microwave device garnets. Applicants alsohave found that certain other high valency ions could also be used onthe tetrahedral of octahedral sites and that a fairly high level ofoctahedral substitution in the garnet structure is preferred in order toobtain magnetic resonance linewidth in the 5 to 20 Oersted range.Moreover, Yttrium displacement is preferably accomplished by addingCalcium in addition to Bismuth to the dodecahedral site. Doping theoctahedral or tetrahedral sites with higher valency ions, preferablygreater than 3+, would allow more Calcium to be introduced to thedodecahedral site to compensate for the charges, which in turn wouldresult in further reduction of Yttrium content.

Modified Synthetic Garnet Compositions:

In one implementation, the modified synthetic garnet composition may berepresented by general Formula I:Bi_(x)Ca_(y+2x)Y_(1−x−y−2z)Fe_(5−y−z)Zr_(y)V_(z)O₁₂, where x=0 to 3, y=0to 1, and z=0 to 1.5, more preferably x=0.5 to 1.4, y=0.3 to 0.55, andz=0 to 0.6. In a preferred implementation, 0.5 to 1.4 formula units ofBismuth (Bi) is substituted for some of the Yttrium (Y) on thedodecahedral site, 0.3 to 0.55 formula units of Zirconium (Zr) issubstituted for some of the Iron (Fe) on the octahedral site. In someembodiments, up to 0.6 formula units of Vanadium (V) is substituted forsome of the Iron (Fe) on the tetrahedral site. Charge balance isachieved by Calcium (Ca) substituting for some or all of the remainingYttrium (Y). In some other embodiments, small amounts of Niobium (Nb)may be placed on the octahedral site and small amounts of Molybdenum(Mo) may be placed on the tetrahedral site.

In another implementation, the modified synthetic garnet composition maybe represented by general Formula II:Bi_(x)Y_(3−x−0.35)Ca_(0.35)Zr_(0.35)Fe_(4.65)O₁₂, where x=0.5 to 1.0,preferably x=0.6 to 0.8, more preferably x=0.5. In this implementation,0.5 to 1.0 formula units of Bismuth (Bi) is substituted for some of theYttrium (Y) on the dodecahedral site and Zirconium (Zr) is substitutedfor some of the Iron (Fe) on the octahedral site. Calcium (Ca²⁺) isadded to the dodecahedral site to replace some of the remaining Y tobalance the Zr charges. Bi content can be varied to achieve varyingmaterial properties while Zr is held fixed at Zr=0.35.

In another implementation, the modified garnet composition may berepresented by general Formula III: Bi(Y,Ca)₂Fe_(4.2)M^(I) _(0.4)M^(II)_(0.4)O₁₂, where M^(I) is the octahedral substitution for Fe and can beselected from one or more of the following elements: In, Zn, Mg, Zr, Sn,Ta, Nb, Fe, Ti, and Sb, where M^(II) is the tetrahedral substitution forFe and can be selected from one or more of the following elements: Ga,W, Mo, Ge, V, Si.

In another implementation, the modified synthetic garnet composition maybe represented by general Formula IV:Y_(2.15−2x)Bi_(0.5)Ca_(0.35+2x)Zr_(0.35)V_(x)Fe_(4.65−x)O₁₂, whereinx=0.1 to 0.8. In this implementation, 0.1 to 0.8 formula units ofVanadium (V) is added to the tetrahedral site to substitute for some ofthe Iron (Fe), and Calcium (Ca) is added to balance the V charges andreplace some of the remaining Y while the levels of Bi and Zr remainfixed similar to Formula III. FIG. 3 illustrates variations of materialproperties in connection with varying levels of V. As shown in FIG. 3,the dielectric constant and density of the material remain largelyconstant with varying levels of V. Increasing levels of V reduces the4PiMs by about 160 Gauss for each 0.1 of V. As further shown in FIG. 3,there are no appreciable changes in 3 dB linewidth up to V=0.5.

In another implementation, the modified synthetic garnet composition maybe represented by Formula V:Bi_(0.9)Ca_(0.9x)Y_(2.1−0.9x)(Zr_(0.7)Nb_(0.1))_(x)Fe_(5−0.8x)O₁₂,wherein x=0.5 to 1.0. In this implementation, the octahedralsubstitution is made with two high valency ions: Zr⁴⁺ and Nb⁵⁺ with Biheld constant at 0.9. FIG. 4 illustrates variations of materialproperties in connection with varying levels of (Zr, Nb). As shown inFIG. 4, the magnetic resonance linewidth decreased with higheroctahedral substitutions. The magnetization also fell as the increase intotal non-magnetic ions overcomes the higher non-magnetic octahedralsubstitutions.

In another implementation, the modified synthetic garnet composition maybe represented by Formula VI:Bi_(0.9)Ca_(0.9+2x)Y_(2.1−0.9−2x)Zr_(0.7)Nb_(0.1)V_(x)Fe_(4.2−x)O₁₂,where V=0-0.6. In this implementation, Vanadium is introduced to theoctahedral site in addition to Zr and Nb. When V=0.6, Y is completelyreplaced. FIGS. 5A-5G illustrate the relationship between firingtemperatures and various material properties as V level increases from 0to 0.6. As illustrated, the 3 dB linewidth, measured in accordance withASTM A883/A883M-01, tends to remain below 50 Oe at all V levels atfiring temperatures below 1040° C. FIG. 6 illustrates the best linewidthat varying firing temperatures versus composition at varying levels of Vof one preferred embodiment. In some implementations, the linewidth canbe further reduced by annealing the material. The effect of annealing onlinewidth of Bi_(0.9)Ca_Zr_(0.7)Nb_(0.1)V_(x)Fe_(4.2−x)O₁₂, where x=0.1to 0.5 is illustrated in Table 1 below.

TABLE 1 Linewidth (Oe) and Curie Temp. (° C.) Data forBi_(0.9)Ca_(0.9+2x)Y_(2.1-0.9-2x)(Zr, Nb)_(0.8)V_(x)Fe _(4.2-x)O₁₂ HeatTreatment Heat Heat (Calcined 3 dB Treatment 3 dB 3 dB Treatment 3 dB 3dB Blend + 3 dB after (Initial before after (Calcined before afterExtended before extended Curie Formula Blend) anneal anneal Blend)anneal anneal Milling) anneal anneal Temp V = 0.5 1050 39 25 1030 38 201030 38 17 108 V = 0.4 1050 44 27 1030 48 18 1030 42 16 112 V = 0.3 105052 32 1030 46 19 1030 48 15 111 V = 0.2 1050 59 43 1030 55 21 1030 62 17108 V = 0.1 1050 78 62 1030 61 24 1030 55 21 107

In another implementation, the modified synthetic garnet composition maybe represented by Formula VI:Bi_(1.4)Ca_(1.05−2x)Zr_(0.55)V_(x)Fe_(4.45−x)O₁₂, where x=0-0.525. Inthis implementation, the level of Bi doping is increased while the levelof octahedral substitution is decreased. The material formed has higherCurie temperature and low linewidth. The Vanadium (V) content is variedfrom 0 to 0.525. When V=0.525, the composition is free of Yttrium. Theresulting material achieved a linewidth of 20 Oe without subsequentlyheat treatment. FIG. 7 illustrates the properties of the material withvarying amount of V. As shown in FIG. 7, V drops the dielectric constantrapidly, about 1 unit for each 0.1 of V in the formula unit, and dropsthe magnetization by about 80 Gauss for each 0.1 of V. Optimizing theprocessing parameters such as firing conditions have produced linewidthas low as 11 or V at or close to 0.525, which is free of Y. These valuesare comparable to commercially available Calcium Yttrium ZirconiumVanadium garnets of the same magnetization.

In another implementation, the modified synthetic garnet composition maybe represented by Formula VII: Y₂CaFe_(4.4)Zr_(0.4)Mo_(0.2)O₁₂. In thisimplementation, high valency ion Molybdenum (Mo) is added to thetetrahedral site to create a single phase crystal. In otherimplementations, the modified synthetic garnet compositions can berepresented by a formula selected from the group consisting of:BiY₂Fe_(4.6)In_(0.4)O₁₂, BiCa_(0.4)Y_(1.6)Fe_(4.6)Zr_(0.4)O₁₂,BiCa_(0.4)Y_(1.6)Fe_(4.6)Ti_(0.4)O₁₂,BiCa_(0.8)Y_(1.2)Fe_(4.6)Sb_(0.4)O₁₂, BiY₂Fe_(4.6)Ga_(0.4)O₁₂,BiCa_(1.2)Y_(0.8)Fe_(4.2)In_(0.4)Mo_(0.4)O₁₂,BiY_(1.2)Ca_(0.8)Fe_(4.2)Zn_(0.4)Mo_(0.4)O₁₂,BiY_(1.2)Ca_(0.8)Fe_(4.2)Mg_(0.4)Mo_(0.4)O₁₂,BiY_(0.4)Ca_(1.6)Fe_(4.2)Zr_(0.4)Mo_(0.4)O₁₂,BiY_(0.4)Ca_(1.6)Fe_(4.2)Sn_(0.4)Mo_(0.4)O₁₂,BiCa₂Fe_(4.2)Ta_(0.4)Mo_(0.4)O₁₂, BiCa₂Fe_(4.2)Nb_(0.4)Mo_(0.4)O₁₂,BiY_(0.8)Ca_(1.2)Fe_(4.6)Mo_(0.4)O₁₂, andBiY_(0.4)Ca_(1.6)Fe_(4.2)Ti_(0.4)Mo_(0.4)O₁₂.

Preparation of the Modified Synthetic Garnet Compositions:

The preparation of the modified synthetic garnet materials can beaccomplished by using known ceramic techniques. A particular example ofthe process flow is illustrated in FIG. 8.

As shown in FIG. 8, the process begins with step 106 for weighing theraw material. The raw material may include oxides and carbonates such asIron Oxide (Fe₂O₃), Bismuth Oxide (Bi₂O₃), Yttrium Oxide (Y₂O₃), CalciumCarbonate (CaCO₃), Zirconium Oxide (ZrO₂), Vanadium Pentoxide (V₂O₅),Yttrium Vanadate (YVO₄), Bismuth Niobate (BiNbO₄), Silica (SiO₂),Niobium Pentoxide (Nb₂O₅), Antimony Oxide (Sb₂O₃), Molybdenum Oxide(MoO₃), Indium Oxide (In₂O₃), or combinations thereof. In oneembodiment, raw material consisting essentially of about 35-40 wt %Bismuth Oxide, more preferably about 38.61 wt %; about 10-12 wt %Calcium Oxide, more preferably about 10.62 wt %; about 35-40 wt % IronOxide, more preferably about 37 wt %, about 5-10 wt % Zirconium Oxide,more preferably about 8.02 wt %; about 4-6 wt % Vanadium Oxide, morepreferably about 5.65 wt %. In addition, organic based materials may beused in a sol gel process for ethoxides and/or acrylates or citratebased techniques may be employed. Other known methods in the art such asco-precipitation of hydroxides may also be employed as a method toobtain the materials. The amount and selection of raw material depend onthe specific formulation.

After the raw material is weighed, they are blended in Step 108 usingmethods consistent with the current state of the ceramic art, which caninclude aqueous blending using a mixing propeller, or aqueous blendingusing a vibratory mill with steel or zirconia media. In someembodiments, a glycine nitrate or spray pyrolysis technique may be usedfor blending and simultaneously reacting the raw materials.

The blended oxide is subsequently dried in Step 110, which can beaccomplished by pouring the slurry into a pane and drying in an oven,preferably between 100-400° C. or by spray drying, or by othertechniques known in the art.

The dried oxide blend is processed through a sieve in Step 112, whichhomogenizes the powder and breaks up soft agglomerates that may lead todense particles after calcining.

The material is subsequently processed through a pre-sintering calciningin Step 114. Preferably, the material is loaded into a container such asan alumina or cordierite sagger and heat treated in the range of about800-1000° C., more preferably about 900-950° C. Preferably, the firingtemperature is low as higher firing temperatures have an adverse effecton linewidth.

After calcining, the material is milled in Step 116, preferably in avibratory mill, an attrition mill, a jet mill or other standardcomminution technique to reduce the median particle size into the rangeof about 0.5 micron to 10 microns. Milling is preferably done in a waterbased slurry but may also be done in ethyl alcohol or another organicbased solvent.

The material is subsequently spray dried in Step 118. During the spraydrying process, organic additives such as binders and plasticizers canbe added to the slurry using techniques known in the art. The materialis spray dried to provide granules amenable to pressing, preferably inthe range of about 10 microns to 150 microns in size.

The spray dried granules are subsequently pressed in Step 120,preferably by uniaxial or isostatic pressing to achieve a presseddensity to as close to 60% of the x-ray theoretical density as possible.In addition, other known methods such as tape casting, tape calendaringor extrusion may be employed as well to form the unfired body.

The pressed material is subsequently processed through a calciningprocess in Step 122. Preferably, the pressed material is placed on asetter plate made of material such as alumina which does not readilyreact with the garnet material. The setter plate is heated in a periodickiln or a tunnel kiln in air or pressure oxygen in the range of betweenabout 850° C.-100° C. to obtain a dense ceramic compact. Other knowntreatment techniques such as induction heat may also be used in thisstep.

The dense ceramic compact is machined in the Step 124 to achievedimensions suitable or the particular applications.

Radio-frequency (RF) applications that utilize synthetic garnetcompositions can include ferrite devices having relatively low magneticresonance linewidths (e.g., approximately 11 Oe or less) as described inreference to FIGS. 2-8. RF applications can also include devices,methods, and/or systems having or related to garnet compositions havingreduced or substantially nil reduced earth content. As described herein,such garnet compositions can be configured to yield relatively highdielectric constants; and such a feature can be utilized to provideadvantageous functionalities. It will be understood that at least someof the compositions, devices, and methods described in reference toFIGS. 2-8 can be applied to such implementations.

FIG. 9 shows a radio-frequency (RF) device 200 having garnet structureand chemistry, and thus a plurality of dodecahedral structures,octahedral structures, and tetrahedral structures. The device 200 caninclude garnet structures (e.g., a garnet structure 220) formed fromsuch dodecahedral, octahedral, and tetrahedral structures. Disclosedherein are various examples of how dodecahedral sites 212, octahedralsites 208, and tetrahedral sites 204 can be filled by or substitutedwith different ions to yield one or more desirable properties for the RFdevice 200. Such properties can include, but are not limited todesirable RF properties and cost-effectiveness of manufacturing ofceramic materials that can be utilized to fabricate the RF device 200.By way of an example, disclosed herein are ceramic materials havingrelatively high dielectric constants, and having reduced orsubstantially nil rare earth contents.

Some design considerations for achieving such features are nowdescribed. Also described are example devices and related RF performancecomparisons. Also described are example applications of such devices, aswell as fabrication examples.

Rare Earth Garnets:

Garnet systems in commercial use typically belong to a series ofcompositions that can be expressed as Y_(3−x)(RE orCa)_(x)Fe_(2−y)(Me)_(y)Fe_(3−z)(Me′)_(z)O₁₂, where “RE” represents anon-Y rare earth element. The non-Y rare earth element (RE) can be, forexample, Gd for temperature compensation of magnetization, with smallamounts of Ho sometimes used for high power doping purposes. Rare earthsare typically trivalent and occupy dodecahedral sites. “Me” inoctahedral sites is typically non-magnetic (e.g., typically Zr⁺⁴,although In⁺³ or Sn⁺⁴ can been used, typically at around y=0.4 in theformula). “Me'” in tetrahedral sites is typically non-magnetic (e.g.,typically Al⁺³ or V⁺⁵, where z can vary from 0 to around 1 in theformula to give a range of magnetizations). Ca⁺² is typically used indodecahedral sites for valency compensation when the octahedral ortetrahedral substitution is an ion of valency>3. Based on the foregoing,one can see that such commercial garnet systems contain greater than 40%Y or other RE elements, with the balance mainly Fe⁺³ on octahedral andtetrahedral sites.

Ferrite Device Design Considerations:

Magnetization (4πM_(s)) of ferrite devices for RF applications such ascellular infrastructure typically operate at 400 MHz to 3 GHz in anabove-resonance mode. To achieve typical bandwidths of about 5 to 15%,magnetizations in a range of approximately 1,000 to 2,000 Gauss(approximately 0.1 to 0.2 Tesla) are desired.

Magnetic losses associated with ferrite devices can be determined by aferrimagnetic resonance linewidth ΔH_(o). Values for such linewidth aretypically less than about 30 Oersted (about 0.377 Ampere-turns/meter),and are typically equivalent to K₁/M_(s), where K₁ is a first ordermagnetocrystalline anisotropy, determined by the anisotropy of the Fe⁺³ion in two of its sites if non-magnetic Y is the only RE. There can alsobe a fractional porosity (p) contribution to linewidth, approximately4πM_(s)×p.

Dielectric losses associated with ferrite devices are typically selectedso that loss tangent δ satisfies a condition tan δ<0.0004. The Curietemperature associated with ferrite devices can be expected to exceedapproximately 160° C. for the above range of magnetizations.

Bismuth Garnets:

Single crystal materials with a formulaBi_((3−2x))Ca_(2x)Fe_(5−x)V_(x)O₁₂ have been grown in the past, where xwas 1.25. A 4πM_(s) value of about 600 Gauss was obtained (which issuitable for some tunable filters and resonators in a 1-2 GHz range),with linewidths of about 1 Oersted, indicating low intrinsic magneticlosses for the system. However, the level of Bi substitution was onlyabout 0.5 in the formula.

Attempts to make single phase polycrystalline materials (with a formulaBi_(3−2x)Ca_(2x)V_(x)Fe_(5−x)O₁₂) similar to the single crystalmaterials were successful only in a region of x>0.96, effectivelyconfining the 4πM_(s) to less than about 700 Oersted and resulting inpoor linewidths (greater than 100 Oersted). Small amounts of Al⁺³reduced the linewidth to about 75 Oersted, but increased Al⁺³ reduced4πM_(s). Bi substitution was only about 0.4 in the formula for thesematerials.

For Faraday rotation devices, the Faraday rotation can be essentiallyproportionate to the level of Bi substitution in garnets, raisinginterest in increasing the level of substitution. Anisotropy isgenerally not a major factor for optical applications, so substitutionon the octahedral and tetrahedral site can be based on maximizing therotation. Thus, in such applications, it may be desirable to introduceas much Bi⁺³ into the dodecahedral site as possible. The maximum levelof Bi⁺³ can be influenced by the size of the dodecahedral rare earthtrivalent ion, and can vary between 1.2 and 1.8 in the formula.

In some situations, the level of Bi⁺³ substitution can be affected bysubstitutions on the other sites. Because Bi⁺³ is non-magnetic, it caninfluence the Faraday rotation through its effect on the tetrahedral andoctahedral Fe⁺³ ions. Since this is thought to be a spin-orbitalinteraction, where Bi⁺³ modifies existing Fe⁺³ pair transitions, one canexpect both a change in the anisotropy of the Fe⁺³ ions and opticaleffects including large Faraday rotation. The Curie temperature of Bi⁺³substituted YIG can also increase at low Bi⁺³ substitution.

Bi Substitution in Polycrystalline Garnets:

To see the effects (e.g., low magnetocrystalline anisotropy and hencelow magnetic losses) that can result from combinations of Bi⁺³ on thedodecahedral site and Zr⁺⁴ on the octahedral site, following approacheswere tested. The first example configuration included fixed Bi andvariable Zr in a formula Bi_(0.5)Y_(2.5−x)Ca_(x)Zr_(x)Fe_(5−x)O₁₂, wherex varied from approximately 0 to 0.35. The second example configurationincluded fixed Zr and variable Bi in a formulaBi_(x)Y_(2.65−x)Ca_(0.35)Zr_(0.35)Fe_(4.65)O₁₂, where x varied fromapproximately 0.5 to 1.4.

FIG. 10 shows various properties as functions of Zr content for thefirst configuration (Bi_(0.5)Y_(2.5−x)Ca_(x)Zr_(x)Fe_(5−x)O₁₂) whereBi⁺³ content was fixed at approximately 0.5 while Zr⁺⁴ content wasvaried from 0 to 0.35. From the plots, one can see that the 0.5 Bimaterial at zero Zr has a relatively high linewidth (near 80 Oe afterporosity correction). This is in contrast to standard Y₃Fe₅O₁₂, whichhas a much lower corrected value of about 17 Oe, indicating thatnon-magnetic Bi⁺³ can substantially raise the magnetocrystallineanisotropy, K₁ contribution from the octahedral and tetrahedral Fe⁺³.

One can also see, as found in Bi-free garnet, that the introduction ofincreasing amounts of Zr⁺⁴ progressively lowers the anisotropycontribution, and very low linewidths are found at Zr=0.35, albeit withsome reduction in Curie temperature. The expected result is a higherCurie temperature from the Bi content being offset by the Zrcontribution.

As further shown in FIG. 10, although the 4πM_(s) value generallyincreases with Zr content, the effect on the K₁/M_(s) contribution isoverwhelmingly on K₁, representing a significant technical breakthrough.

FIG. 11 shows various properties as functions of Bi content for thesecond configuration (Bi_(x)Y_(2.65−x)Ca_(0.35)Zr_(0.35)Fe_(4.65)O₁₂)where Zr⁺⁴ content was fixed at approximately 0.35 while Bi⁺³ contentwas varied. FIG. 12 shows dielectric constant and density as functionsof Bi content for the same configuration. One can see that a largeincrease in dielectric constant occurs when Bi content is greater thanapproximately 1. In some implementations, such an increased dielectricconstant can be utilized to yield RF devices having desirable features.

It appeared that the maximum Bi⁺³ content was 1.4 in the formula, andtherefore can be a optimum or desired amount to replace Y⁺³, at least inthe range of Zr⁺⁴ substitution examined. At the example desired Bicontent of 1.4, there was a desire to optimize the Zr⁺⁴ content toreduce or minimize the linewidth without substantially reducing theCurie temperature. Also considered was a possibility of implementing arange of V⁺⁵ substitutions which can yield a range of magnetizationswithout much reduction in Curie temperature (e.g., as found in Y-basedZr or In Ca—V garnets).

Based at least in part on the foregoing, the following substitutionswere tested to optimize or improve Bi-substituted garnet compositions.For example, by using Ca⁺² to balance V⁺⁵, more Y could be displaced, ata rate of 2 Ca⁺² for 1 V⁺⁵. In another example, Zr⁺⁴ can yield 1:1substitution of Ca⁺² for Y; thus, if Nb⁺⁵ could be used instead on theoctahedral site, more Y could be removed from the compositions.

FIG. 13 shows plots of various properties as functions of Zr contentthat extends beyond the 0.35 limit described in reference to FIG. 10.Such measurements were based on the foregoing selection of Bi content(approximately 1.4) to refine or optimize the Zr content. Based on suchmeasurements, an example Zr content of 0.55 was selected to test effectsof variation of V⁺⁵ content.

FIG. 14 shows plots of various properties as functions of v+5 content.For such measurements, Bi content was held as approximately 1.4, and Zrcontent was held at approximately 0.55. It is noted that at the maximumV⁺⁵ substitution, the example composition(Bi_(1.4)Ca_(1.6)Zr_(0.55)V_(0.525)Fe_(3.925)O₁₂) is substantially freeof rare earth.

In the context of RF applications, following observations can be madefor the foregoing example rare earth-free composition(Bi_(1.4)Ca_(1.6)Zr_(0.55)V_(0.525)Fe_(3.925)O₁₂). Dielectric constantis approximately 27; and this is thought to be due to the “lone pair” ofelectrons on Bi⁺³ which can greatly increase the polarizability of theion. Dielectric loss is less than 0.0004, which is useful for mostapplications. Magnetic loss (as linewidth) is approximately 11 Oersted,which is comparable with the best Y based garnets. 4πM_(s) isapproximately 1150 Gauss, which is useful for many RF devices such asthose used in cellular infrastructures. Curie temperature isapproximately 160° C., which is useful for most applications.

Examples of Devices Having Rare Earth Free or Reduced Garnets:

As described herein, garnets having reduced or no rare earth content canbe formed, and such garnets can have desirable properties for use indevices for applications such as RF applications. In someimplementations, such devices can be configured to take advantage ofunique properties of the Bi⁺³ ion.

For example, the “lone pair” of electrons on the Bi⁺³ ion can raise theionic polarizability and hence the dielectric constant. This isconsistent with the measurement observed in reference to FIG. 14. Inthat example, the dielectric constant roughly doubled, from 15 to 27 asone went from standard YCaZrV garnets to BiCaZrV garnets when Bi was atmaximum substitution at 1.4 in the formula. Such an increase indielectric constant can be utilized in a number of ways.

For example, because the center frequency of a ferrite device (such as agarnet disk) operating in a split polarization transverse magnetic (TM)mode is proportional to 1/(ε)^(1/2), doubling the dielectric constant(ε) can reduce the frequency by a factor of square root of 2(approximately 1.414). As described herein in greater detail, increasingthe dielectric constant by, for example, a factor of 2, can result in areduction in a lateral dimension (e.g., diameter) of a ferrite disk byfactor of square root of 2. Accordingly, the ferrite disk's area can bereduced by a factor of 2. Such a reduction in size can be advantageoussince the device's footprint area on an RF circuit board can be reduced(e.g., by a factor of 2 when the dielectric constant is increased by afactor of 2). Although described in the context of the example increaseby a factor of 2, similar advantages can be realized in configurationsinvolving factors that are more or less than 2.

Reduced Size Circulators/Isolators Having Ferrite with High DielectricConstant:

As described herein, ferrite devices having garnets with reduced or norare earth content can be configured to include a high dielectricconstant property. Various design considerations concerning dielectricconstants as applied to RF applications are now described. In someimplementations, such designs utilizing garnets with high dielectricconstants may or may not necessarily involve rare earth freeconfigurations.

Values of dielectric constant for microwave ferrite garnets and spinelscommonly fall in a range of 12 to 18 for dense polycrystalline ceramicmaterials. Such garnets are typically used for above ferromagneticresonance applications in, for example, UHF and low microwave region,because of their low resonance linewidth. Such spinels are typicallyused at, for example, medium to high microwave frequencies, for belowresonance applications, because of their higher magnetization. Most, ifnot substantially all, circulators or isolators that use such ferritedevices are designed with triplate/stripline or waveguide structures.

Dielectric constant values for low linewidth garnets is typically in arange of 14 to 16. These materials can be based on Yttrium iron garnet(YIG) with a value of approximately 16, or substituted versions of thatchemistry with Aluminum or, for example, Zirconium/Vanadium combinationswhich can reduce the value to around 14. Although for example LithiumTitanium based spinel ferrites exist with dielectric constants up toclose to 20, these generally do not have narrow linewidths; and thus arenot suitable for many RF applications.

As described herein, garnets made using Bismuth substituted for Yttriumcan have much higher dielectric constants. Also as described herein,when Zirconium is used in tandem with Bismuth substitution to maintainlow linewidths, then the dielectric constant of the garnet can increaseas shown by way of examples in Table 2.

TABLE 2 Den- Dielectric 4πM_(s) Linewidth sity Composition Constant(Gauss) (Oersted) (g/cc) Bi_(0.5)Ca_(0.35)Y_(2.15)Zr_(0.35)Fe_(4.65)O₁₂18.93 1985 25 5.485 Bi_(0.9)Ca_(0.35)Y_(1.75)Zr_(0.35)Fe_(4.65)O₁₂ 21.351925 67 5.806 Bi_(1.4)Ca_(0.35)Y_(1.25)Zr_(0.35)Fe_(4.65)O₁₂ 31.15 185752 6.041

Table 2 shows that it is possible to more than double the dielectricconstant of garnets. In some implementations, an increase in dielectricconstant can be maintained for compositions containing Bismuth,including those with other non-magnetic substitution on either or bothof the octahedral and tetrahedral sites (e.g., Zirconium or Vanadium,respectively). By using ions of higher polarization, it is possible tofurther increase the dielectric constant. For example, Niobium orTitanium can be substituted into the octahedral or tetrahedral site; andTitanium can potentially enter both sites.

In some implementations, a relationship between ferrite device size,dielectric constant, and operating frequency can be represented asfollows. There are different equations that can characterize differenttransmission line representations. For example, in above-resonancestripline configurations, the radius R of a ferrite disk can becharacterized asR=1.84/[2π(effective permeability)×(dielectric constant)]^(1/2)  (1)where (effective permeability)=H_(dc)+4πM_(s)/H_(dc), with H_(dc) beingthe magnetic field bias. Equation 1 shows that, for a fixed frequencyand magnetic bias, the radius R is inversely proportional to the squareroot of the dielectric constant.

In another example, in below-resonance stripline configurations, arelationship for ferrite disk radius R similar to Equation 1 can beutilized for weakly coupled quarter wave circulators where the low biasfield corresponds to below-resonance operation. For below-resonancewaveguide configurations (e.g., in disk or rod waveguides), both lateraldimension (e.g., radius R) and thickness d of the ferrite can influencethe frequency. However, the radius R can still be expressed asR=λ/[2π(dielectric constant)^(1/2)][((πR)/(2d))²+(1.84)²]^(1/2),  (2)which is similar to Equation 1 in terms of relationship between R anddielectric constant.

The example relationship of Equation 2 is in the context of a circulardisk shaped ferrites. For a triangular shaped resonator, the samewaveguide expression can used, but in this case, A (altitude of thetriangle) being equal to 3.63×λ/2π applies instead of the radius in thecircular disk case.

In all of the foregoing example cases, one can see that by increasingthe dielectric constant (e.g., by a factor of 2), one can expect toreduce the size of the ferrite (e.g., circular disk or triangle) by afactor of square root of 2, and thereby reduce the area of the ferriteby a factor of 2. As described in reference to Equation 2, thickness ofthe ferrite can also be reduced.

In implementations where ferrite devices are used as RF devices, sizesof such RF devices can also be reduced. For example, in a striplinedevice, a footprint area of the device can be dominated by the area ofthe ferrite being used. Thus, one can expect that a correspondingreduction in device size would be achieved. In a waveguide device, adiameter of the ferrite being used can be a limiting factor indetermining size. However, a reduction provided for the ferrite diametermay be offset by the need to retain waveguide-related dimensions in themetal part of the junction.

Examples of Reduced-Size Ferrite Having Yttrium Free Garnet:

As described herein, ferrite size can be reduced significantly byincreasing the dielectric constant associated with garnet structures.Also as described herein, garnets with reduced Yttrium and/or reducednon-Y rare earth content can be formed by appropriate Bismuthsubstitutions. In some embodiments, such garnets can includeYttrium-free or rare earth free garnets. An example RF device havingferrite devices with increased dielectric constant and Yttrium-freegarnets is described in reference to FIGS. 15-17.

FIGS. 15A and 15B summarize the example ferrite size reductionsdescribed herein. As described herein and shown in FIG. 15A, a ferritedevice 200 can be a circular-shaped disk having a reduced diameter of2R′ and a thickness of d′. The thickness may or may not be reduced. Asdescribed in reference to Equation 1, the radius R of a circular-shapedferrite disk can be inversely proportional to the square root of theferrite's dielectric constant. Thus, the increased dielectric constantof the ferrite device 200 is shown to yield its reduced diameter 2R′.

As described herein and shown in FIG. 15B, a ferrite device 200 can alsobe a triangular-shaped disk having a reduced side dimension of S′ and athickness of d′. The thickness may or may not be reduced. As describedin reference to Equation 2, the altitude A of a triangular-shapedferrite disk (which can be derived from the side dimension S) can beinversely proportional to the square root of the ferrite's dielectricconstant. Thus, the increased dielectric constant of the ferrite device200 is shown to yield its reduced dimension S′.

Although described in the context of example circular and triangleshaped ferrites, one or more features of the present disclosure can alsobe implemented in other shaped ferrites.

To demonstrate the foregoing effect of the dielectric constant on theoperating frequency (and size in some implementations), circulator(sometimes also referred to as an isolator) devices were built. Onecirculator was built with a current ferrite available as TransTechTTVG1200 (17.56 mm diameter, 1 mm thickness). Another circulator wasbuilt with a Yttrium free ferrite with the same dimensions. For thepurpose of description, such a Yttrium free ferrite is referred to as“TTHiE1200.” Each of the two example circulators has a diameter of about25 mm.

The TTVG1200 ferrite has a Yttrium Calcium Zirconium Vanadium Irongarnet configuration, and a typical dielectric constant of approximately14.4. The Yttrium free ferrite (TTHiE1200) has a Bismuth CalciumZirconium Vanadium Iron garnet configuration containing not more thanapproximately 1% rare earth oxides, and a dielectric constant ofapproximately 26.73.

Additional details concerning the foregoing example circulators aredescribed in reference to FIGS. 16A and 16B, in which a “ferrite” can bethe first type (TTVG1200) or the second type (TTHiE1200).

FIGS. 16A and 16B show an example of a circulator 300 having a pair offerrite disks 302, 312 disposed between a pair of cylindrical magnets306, 316. Each of the ferrite disks 302, 312 can be a ferrite diskhaving one or more features described herein. FIG. 16A shows anun-assembled view of a portion of the example circulator 300. FIG. 16Bshows a side view of the example circulator 300.

In the example shown, the first ferrite disk 302 is shown to be mountedto an underside of a first ground plane 304. An upper side of the firstground plane 304 is shown to define a recess dimensioned to receive andhold the first magnet 306. Similarly, the second ferrite disk 312 isshown to be mounted to an upper side of a second ground plane 314; andan underside of the second ground plane 314 is shown to define a recessdimensioned to receive and hold the second magnet 316.

The magnets 306, 316 arranged in the foregoing manner can yieldgenerally axial field lines through the ferrite disks 302, 312. Themagnetic field flux that passes through the ferrite disks 302, 312 cancomplete its circuit through return paths provided by 320, 318, 308 and310 so as to strengthen the field applied to the ferrite disks 302, 312.In some embodiments, the return path portions 320 and 310 can be diskshaving a diameter larger than that of the magnets 316, 306; and thereturn path portions 318 and 308 can be hollow cylinders having an innerdiameter that generally matches the diameter of the return path disks320, 310. The foregoing parts of the return path can be formed as asingle piece or be an assembly of a plurality of pieces.

The example circulator device 300 can further include an inner fluxconductor (also referred to herein as a center conductor) 322 disposedbetween the two ferrite disks 302, 312. Such an inner conductor can beconfigured to function as a resonator and matching networks to the ports(not shown).

FIG. 17 shows insertion loss plots and return loss plots for the twoabove-described 25 mm circulators (based on the TTVG1200 ferrite(YCaZrVFe garnet, dielectric constant of 14.4), and based on the Yttriumfree ferrite (TTHiE1200) (BiCaZrVFe garnet, dielectric constant of26.73)). Frequencies and loss values for edges of the loss curves of thetwo circulators (“TTVG1200” and “TTHiE1200”) are indicated by theirrespective trace markers shown in FIG. 17 and listed in Table 3.

TABLE 3 Marker Trace Frequency Loss value 1 Insertion loss (Y-freeTTHiE1200) 1.77 GHz  −0.40 dB 2 Insertion loss (Y-free TTHiE1200) 2.23GHz  −0.39 dB 3 Insertion loss (TTVG1200) 2.41 GHz  −0.39 dB 4 Insertionloss (TTVG1200) 3.01 GHz  −0.41 dB 5 Return loss (Y-free TTHiE1200) 1.77GHz −19.87 dB 6 Return loss (Y-free TTHiE1200) 2.23 GHz −16.64 dB 7Return loss (TTVG1200) 2.41 GHz −16.37 dB 8 Return loss (TTVG1200) 3.01GHz −18.75 dB

Based on the foregoing measurements, one can see that the TTVG1200configuration has a center operating frequency of about 2.7 GHz, and theTTHiE1200 configuration has a center operating frequency of about 2.0GHz. The ratio of center operating frequencies between TTHiE1200 andTTVG1200 configurations is approximately 0.74. It is noted that atheoretical reduction in frequency due to a higher dielectric constantcan be calculated (e.g., using Bosma's equations) as being proportionalto square root of the ratios of the dielectric constants. Thus, such acalculation yields sqrt(14.4/26.73)=0.734, which is in good agreementwith the measured reduction of 0.74.

For the example 25 mm circulators having the TTHiE1200 and TTVG1200configurations, a comparison of intermodulation yields the followingmeasurements. For 2×40 W tones at room temperature, the TTVG1200configuration yields an intermodulation performance of approximately −78dBc at 2.7 GHz, and the TTHiE1200 configuration yields anintermodulation performance of approximately −70 dBc at 1.8 GHz. It isnoted that such results are expected due to the reduction in the biasingmagnetic field.

To further characterize the TTHiE1200 ferrite as described herein, asmaller 10 mm circulator was made using a TTHiE1200 ferrite disk (radiusof approximately 7.00 mm, thickness of approximately 0.76 mm). FIGS. 18Aand 18B show s-parameter data for the 10 mm device at operatingtemperatures of 25° C. and 100° C., respectively. Intermodulationmeasurements were also made for the 10 mm device at 25° C. For 2×15 Wtones, intermodulation values are listed in Table 4, where variousparameters are indicated in the “Parameter” column.

TABLE 4 Intermodulation Parameter (dBc) 2 × 15 W @ 2110 & 2115 MHz,−59.9 3^(rd) Order IMD @ 2105 MHz 2 × 15 W @ 2110 & 2115 MHz, −58.83^(rd) Order IMD @ 2120 MHz 2 × 15 W @ 2138 & 2143 MHz, −57.5 3^(rd)Order IMD @ 2133 MHz 2 × 15 W @ 2138 & 2143 MHz, −56.7 3^(rd) Order IMD@ 2148 MHz 2 × 15 W @ 2165 & 2170 MHz, −56.0 3^(rd) Order IMD @ 2160 MHz2 × 15 W @ 2165 & 2170 MHz, −54.9 3^(rd) Order IMD @ 2175 MHz

Based on FIGS. 18A and 18B, one can see that the s-parameter dataappears to be generally positive. Based on Table 4, IMD performance isgenerally what is expected for this size package. For example, typicalIMD performance for a 20 mm device is about −70 dBc, and about −60 dBcfor a 15 mm device.

Various examples of new garnet systems and devices related thereto aredescribed herein. In some embodiments, such garnet systems can containhigh levels of Bismuth, which can allow formation of low loss ferritedevices. Further, by selected addition of other elements, one can reduceor eliminate rare earth content of garnets, including commercialgarnets. Reduction or elimination of such rare earth content caninclude, but is not limited to, Yttrium. In some embodiments, the garnetsystems described herein can be configured to significantly increase(e.g., double) the dielectric constant of non-Bi garnets, therebyoffering the possibility of significantly decreasing (e.g., halving) theprinted circuit “footprint” of ferrite devices associated withconventional garnets.

In some implementations as described herein, a synthetic garnet materialcan include a structure having dodecahedral sites, with Bismuthoccupying at least some of the dodecahedral sites. In some embodiments,such a garnet material can have a dielectric constant value of at least18.0, 19.0, 20.0, 21.0, 22.0, 23.0, 24.0, 25.0, 26.0, or 27.0.

In some embodiments, ferrite-based circulator devices having one or morefeatures as described herein can be implemented as a packaged modulardevice. FIG. 19 shows an example packaged device 400 having a circulatordevice 300 mounted on a packaging platform 404 and enclosed by a housingstructure 402. The example platform 404 is depicted as including aplurality of holes 408 dimensioned to allow mounting of the packageddevice 400. The example packaged device 400 is shown further includeexample terminals 406 a-406 c configured to facilitate electricalconnections.

In some embodiments, a packaged circulator/isolator such as the exampleof FIG. 19 can be implemented in a circuit board or module. Such acircuit board can include a plurality of circuits configured to performone or more radio-frequency (RF) related operations. The circuit boardcan also include a number of connection features configured to allowtransfer of RF signals and power between the circuit board andcomponents external to the circuit board.

In some embodiments, the foregoing example circuit board can include RFcircuits associated with a front-end module of an RF apparatus. As shownin FIG. 20, such an RF apparatus can include an antenna 412 that isconfigured to facilitate transmission and/or reception of RF signals.Such signals can be generated by and/or processed by a transceiver 414.For transmission, the transceiver 414 can generate a transmit signalthat is amplified by a power amplifier (PA) and filtered (Tx Filter) fortransmission by the antenna 412. For reception, a signal received fromthe antenna 412 can be filtered (Rx Filter) and amplified by a low-noiseamplifier (LNA) before being passed on to the transceiver 414. In theexample context of such Tx and Rx paths, circulators and/or isolators400 having one or more features as described herein can be implementedat or in connection with, for example, the PA circuit and the LNAcircuit.

In some embodiments, circuits and devices having one or more features asdescribed herein can be implemented in RF applications such as awireless base-station. Such a wireless base-station can include one ormore antennas 412, such as the example described in reference to FIG.20, configured to facilitate transmission and/or reception of RFsignals. Such antenna(s) can be coupled to circuits and devices havingone or more circulators/isolators as described herein.

As described herein, terms “circulator” and “isolator” can be usedinterchangeably or separately, depending on applications as generallyunderstood. For example, circulators can be passive devices utilized inRF applications to selectively route RF signals between an antenna, atransmitter, and a receiver. If a signal is being routed between thetransmitter and the antenna, the receiver preferably should be isolated.Accordingly, such a circulator is sometimes also referred to as anisolator; and such an isolating performance can represent theperformance of the circulator.

FIGS. 21-25 show examples of how ferrite devices having one or morefeatures as described herein can be fabricated. FIG. 16 shows a process20 that can be implemented to fabricate a ceramic material having one ormore of the foregoing properties. In block 21, powder can be prepared.In block 22, a shaped object can be formed from the prepared powder. Inblock 23, the formed object can be sintered. In block 24, the sinteredobject can be finished to yield a finished ceramic object having one ormore desirable properties.

In implementations where the finished ceramic object is part of adevice, the device can be assembled in block 25. In implementationswhere the device or the finished ceramic object is part of a product,the product can be assembled in block 26.

FIG. 21 further shows that some or all of the steps of the exampleprocess 20 can be based on a design, specification, etc. Similarly, someor all of the steps can include or be subjected to testing, qualitycontrol, etc.

In some implementations, the powder preparation step (block 21) of FIG.21 can be performed by the example process described in reference toFIG. 14. Powder prepared in such a manner can include one or moreproperties as described herein, and/or facilitate formation of ceramicobjects having one or more properties as described herein.

In some implementations, powder prepared as described herein can beformed into different shapes by different forming techniques. By way ofexamples, FIG. 22 shows a process 50 that can be implemented topress-form a shaped object from a powder material prepared as describedherein. In block 52, a shaped die can be filled with a desired amount ofthe powder. In FIG. 23, configuration 60 shows the shaped die as 61 thatdefines a volume 62 dimensioned to receive the powder 63 and allow suchpower to be pressed. In block 53, the powder in the die can becompressed to form a shaped object. Configuration 64 shows the powder inan intermediate compacted form 67 as a piston 65 is pressed (arrow 66)into the volume 62 defined by the die 61. In block 54, pressure can beremoved from the die. In block 55, the piston (65) can be removed fromthe die (61) so as to open the volume (62). Configuration 68 shows theopened volume (62) of the die (61) thereby allowing the formed object 69to be removed from the die. In block 56, the formed object (69) can beremoved from the die (61). In block 57, the formed object can be storedfor further processing.

In some implementations, formed objects fabricated as described hereincan be sintered to yield desirable physical properties as ceramicdevices. FIG. 24 shows a process 70 that can be implemented to sintersuch formed objects. In block 71, formed objects can be provided. Inblock 72, the formed objects can be introduced into a kiln. In FIG. 25,a plurality of formed objects 69 are shown to be loaded into a sinteringtray 80. The example tray 80 is shown to define a recess 83 dimensionedto hold the formed objects 69 on a surface 82 so that the upper edge ofthe tray is higher than the upper portions of the formed objects 69.Such a configuration allows the loaded trays to be stacked during thesintering process. The example tray 80 is further shown to definecutouts 83 at the side walls to allow improved circulation of hot gas atwithin the recess 83, even when the trays are stacked together. FIG. 25further shows a stack 84 of a plurality of loaded trays 80. A top cover85 can be provided so that the objects loaded in the top tray generallyexperience similar sintering condition as those in lower trays.

In block 73, heat can be applied to the formed objects so as to yieldsintered objects. Such application of heat can be achieved by use of akiln. In block 74, the sintered objects can be removed from the kiln. InFIG. 25, the stack 84 having a plurality of loaded trays is depicted asbeing introduced into a kiln 87 (stage 86 a). Such a stack can be movedthrough the kiln (stages 86 b, 86 c) based on a desired time andtemperature profile. In stage 86 d, the stack 84 is depicted as beingremoved from the kiln so as to be cooled.

In block 75, the sintered objects can be cooled. Such cooling can bebased on a desired time and temperature profile. In block 206, thecooled objects can undergo one or more finishing operations. In block207, one or more tests can be performed.

Heat treatment of various forms of powder and various forms of shapedobjects are described herein as calcining, firing, annealing, and/orsintering. It will be understood that such terms may be usedinterchangeably in some appropriate situations, in context-specificmanners, or some combination thereof.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A modified garnet structure comprising: abismuth-doped garnet represented by the formulaBi_(3−x)(Ca)_(x)Fe_(2−y)(Me)_(y)Fe_(3−z)(Me′)_(z)O₁₂, x being greaterthan or equal to 1.6 and less than or equal to 2.0, , y being greaterthan or equal to 0.35 and less than or equal to 0.75, z being greaterthan 0 and less than or equal to 0.525, and each of Me and Me′representing a metal element.
 2. The modified garnet structure of claim1 wherein the dielectric constant value is at least
 21. 3. The modifiedgarnet structure of claim 1 wherein the dielectric constant value is atleast
 27. 4. The modified garnet structure of claim 1 wherein the metalelement Me includes Zr.
 5. The modified garnet structure of claim 1wherein the metal element Me′ includes V.
 6. The modified garnetstructure of claim 1 wherein the bismuth-doped garnet is substantiallyfree of rare earth elements.
 7. The modified garnet structure of claim 1wherein the garnet material has a ferrimagnetic resonance linewidthvalue that is less than 12 Oersted.
 8. A modified garnet structurecomprising: a bismuth-doped garnet represented by the formulaBi_(1.4)Ca_(1.6)Zr_(0.55)V_(0.525)Fe_(3.925)O₁₂, the bismuth-dopedgarnet material having a dielectric constant value of at least
 21. 9.The modified garnet structure of claim 8 wherein the bismuth-dopedgarnet has a dielectric constant value of at least
 27. 10. The modifiedgarnet structure of claim 8 wherein the garnet material has aferrimagnetic resonance linewidth value that is less than 12 Oersted.11. A radiofrequency system comprising: at least one circulatorincluding a bismuth-doped garnet material represented by the formulaBi_(3−x)(Ca)_(x)Fe_(2−y)(Me)_(y)Fe_(3−z)(ME′)_(z)O₁₂, x being greaterthan or equal to 1.6 and less than or equal to 2.0, y being greater thanor equal to 0.35 and less than or equal to 0.75, z being greater than orequal to 0 and less than or equal to 0.525, and each of Me and Me′representing a metal element.
 12. The radiofrequency device of claim 11wherein the circulator is incorporated into an antenna.
 13. Theradiofrequency device of claim 11 wherein the system is a base station.14. The radiofrequency device of claim 11 wherein the bismuth-dopedgarnet material has a dielectric constant value of at least
 21. 15. Theradiofrequency device of claim 11 wherein the dielectric constant valueis at least
 27. 16. The radiofrequency device of claim 11 wherein themetal element Me includes Zr.
 17. The radiofrequency device of claim 11wherein the metal element Me′ includes V.
 18. The radiofrequency deviceof claim 11 wherein the bismuth-doped garnet is substantially free ofrare earth elements.
 19. The radiofrequency device of claim 11 whereinthe garnet material has a ferrimagnetic resonance linewidth value thatis less than 12 Oersted.
 20. The radiofrequency device of claim 11wherein garnet material has a compositionBi_(1.4)Ca_(1.6)Zr_(0.55)V_(0.525)Fe_(3.925)O₁₂.